This application claims priority from Korean Patent Application No. 2004-0088915, filed on Nov. 3, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a fluid dynamic bearing for supporting a rotating body and a hard disk drive (HDD) employing the fluid dynamic bearing and, more particularly, to a fluid dynamic bearing constructed to support stably a rotating body on which an non-uniform force is applied, and an HDD employing the fluid dynamic bearing.
2. Description of the Related Art
Hard disk drives (HDDs) information storage devices that reproduce data stored in a disk or record data on the disk using a read/write head. In the HDDs, the read/write head functions by being moved by an actuator to a desired position a predetermined height above a recording surface of the rotating disk.
With recent industrial development, HDDs are being employed in various types of electronic devices, such as mobile phones, MP3 players, and game devices. To this end, there is a demand for compact and slim HDDs.
As an effort to make HDDs slim, a single-head HDD in which a hard disk has one recording surface and a single head which faces the recording surface has been disclosed.
FIG. 1 is a schematic cross-sectional view illustrating essential parts of a conventional single-head HDD. FIG. 2 is a bottom view of a thrust bearing part of the single-head HDD of FIG. 1. FIG. 3 is a sectional view of the thrust bearing part taken along line III-III of FIG. 2.
Referring to FIGS. 1 through 3, the conventional single-head HDD includes a fluid dynamic bearing 10, a rotary shaft 20 rotatably inserted into the fluid dynamic bearing 10, a hard disk 30 installed on the rotary shaft 20 and having one recording surface 31, a driving source 40 providing a rotational force to the hard disk 30, and a head 50 recording and reproducing information on the hard disk 30.
The rotary shaft 20 is located at a center of rotation of the hard disk 30 through a rotor housing 25, and includes a journal part 21 supported in a radial direction and a thrust part 23 supported in a longitudinal direction of the rotary shaft 20 by the fluid dynamic bearing 10.
The fluid dynamic bearing 10 has a hollow space 10a into which the rotary shaft 20 is rotatably inserted, and includes a journal bearing part 11 formed along an outer circumference of the journal part 21 and a thrust bearing part 15 facing the thrust part 23 and supporting the rotary shaft 20 in the longitudinal direction of the rotary shaft 20.
Referring to FIGS. 2 and 3, the thrust bearing part 15 has an annular shape, and includes a plurality of grooves 17 formed on a surface thereof facing the thrust part 23 (see FIG. 1). As shown in FIGS. 2 and 3, each of the plurality of grooves 17 has a symmetric spiral pattern having the same shape and arrangement. That is, when a tangent line 15a touching an outer circumferential surface of the thrust bearing part 15 and a line segment 17a extending from a groove 17 form a groove angle θG therebetween, all the grooves 17 have the same groove angle of θG. Further, when the thrust bearing unit 15 is sectioned taken along line III-III of FIG. 2, all the grooves 17 have the same groove width dg, and ridges 19, each of which is disposed between adjacent grooves 17, have the same width dr. Accordingly, if the rotary shaft 20 is positioned at the center of rotation of the hard disk 30 and a uniform load is applied to the hard disk 30, the rotary shaft 20 is stably supported by the same force indicated by arrows 63a and 63b in the longitudinal direction.
The driving source 40 includes a magnet 41 disposed inside the rotor housing 25 and a stator core 45 formed along an outer circumference of the fluid dynamic bearing 10. The driving source 40 rotates the hard disk 30 using an electromagnetic force generated by applying current to the stator core 45.
The head 50 is disposed on a slider installed at one end of a suspension 55, and is reciprocated by an actuator (not shown) in a predetermined area over the recording surface 31 to record and reproduce information on the recording surface 31. The slider is lifted when the hard disk 30 rotates, and the head 50 is maintained at a predetermined height H due to a gram load 61 applied to the suspension 55. Here, a force 62 counteracting a force of lifting the head 50 is applied to the hard disk 30 in a direction opposite to a direction in which the head 50 is lifted.
Accordingly, as shown, when the HDD employs the single head to be made compact, an unbalanced force is applied to the hard disk 30 due to the counteractive force 62 between the head 50 and the hard disk 30. In the meantime, when the thrust bearing part 15 with the symmetric structure is used, the hard disk 30 and the rotary shaft 20 slantingly rotate in an unstable state due to the unbalanced force applied to the hard disk 30, as shown by a two dot and dash line in FIG. 1. Thus, information recording and reproduction performances deteriorate and noises are caused.